The cellular regulation of transition metals is necessary for the normal cell growth. Most metals are required only at low levels and when present in higher amounts, removal of these metals must occur or toxicity results. Therefore most cells have metal detoxification systems in place either to tightly control metal levels or in the case of certain metals like mercury, to rid the cell of the metal completely. Copper is a transition metal that belongs in the former category. Systems involved in copper homeostasis are now just beginning to be understood and one important link between copper regulation and oxygen radical mediated toxicity has been discovered. Expression of a newly discovered protein, ATX1, in superoxide dismutase deficient (SOD) yeast appears to protect cells against the damage from superoxide and hydrogen peroxide although the mechanism is unknown. The research in this proposal deals with understanding how ATX 1 can reverse this toxicity. ATX1 contains a heavy metal binding motif thought to be involved in copper binding and has high sequence homology to several other metal binding proteins. One of the goals of this proposal involves the characterization of the metal coordination environment in ATX1 by using several spectroscopic tools including NMR spectroscopy. Both the metal site and the protein structure can be examined by using heteronuclear techniques. As a result, knowledge from this investigation will shed light onto how ATX1 can reverse oxygen radical toxicity as well as provide information regarding the active site of a new perhaps novel copper binding protein.